The subject invention is directed to the mechanical dampener art and, more particularly, to a rotational damper for use in motor vehicle applications to enable the smooth motion of spring-loaded accessory components and will be described with particular reference thereto. However, it is to be understood that the invention has broader application and is useful as an interface to reduce jerky motion and vibrations or oscillations between any pair of mechanical parts that are rotated with respect to each other.
Viscous dampers have, in the past, been widely used to reduce oscillations and vibrations between moving parts. In those devices, a set of vanes on a turning rotor act against a fluid dampening medium to generate a counter moment or resistance which is used for dampening purposes. Fluids having a relatively high viscosity such as, for example, silicone oil are often used as the dampening medium because of their relatively stable nature and good performance characteristics. Viscous damping devices of this type are commercially readily available and widely used.
One problem, however, with dampers based on flowable mediums, is that they are difficult to manufacture, relatively expensive, and oftentimes sensitive to variations in temperature. In order to prevent the dampening fluid from leaking from the device housing, various seals or the like must be incorporated into the dampener design, adding to its complexity and overall increased cost. It is difficult to manufacture such dampers because the tolerances between the seals and sealing surfaces must be precisely controlled. Further, it is difficult to control the dependency of the fluid medium viscosity on the temperature of the device particularly as the device heats up during use.
As an alternative, various rotational dampers have been proposed which are purely mechanical in nature. One such device is taught in U.S. Pat. No. 5,605,208 wherein a disk-shaped rotor is supported within a housing together with an annular friction surface, the rotor being axially pressed by a spring member against the friction surface within the housing to establish a dampening interface therebetween. According to this construction, the braking moment between the rotor and the friction surface is primarily established by the force of the spring member acting against the rotor. The counter force may therefore be varied by controlling the tension on the spring member or, alternatively, through selection of alternative materials having various coefficients of friction for use as the frictional material.
One problem with the above design, however, is that the spring member adds to the overall cost of the device and, in addition, makes manufacture thereof more difficult because the spring must be precisely positioned within the device. In addition, the device is sensitive to the spring constant, or spring force, of the biasing spring which may lead to loss of dampening effect as the spring ages during use.
Further with regard to the above device, only a single side surface of the frictional material is used to provide a dampening interface between the movable rotor member and the fixed housing member. The second side surface of the frictional material is used to secure the frictional material to the housing member and, thus, is wasted with respect to its potential use as a second dampening interface between the frictional material and the housing member for providing an additional second dampening effect.